Abstract: According to the deloyment of State Council the demands on greatly developing energy and land saving buildingsand building up a saving society, it should be implemented the standard of building energy -saving 50% all over the country,so as to impel the execution of energy saving 65% standard of urban residetial buildings. Many cities are establishing orhave carried out the dwelling building energy saving 65% standard in China. How could building energy -saving index bechanged into envelope thermal property index? It should be analyzed the situation of existing buildings under energy saving50% standard and be got a reasonable design method to improve energy -saving technology. Combining the situation of thebuildingsin Xi? an, it will be found out the gap between thermal property index of existing buildings and new designstandard, and several mending measures will be proposed.